It turns out that cattle has a symbiosis with land, just like Joel Salatin already demonstrated on his Polyface Farm, meaning desert land can be reclaimed by grazing it with carefully managed herds of cattle. Using this strategy it seems we can really return our atmosphere to pre industrial CO2 levels.
Doing this would require some kind of herd management device, probably a digital solar driven device that can be used to keep herds in certain places, for lack of electrical fencing (as Joel Salatin uses).